The present proposal represents an expanded effort of that undertaken in the 1992-93 FY, which was entitled "Investigation of trace metal sequestering by polyphosphate bodies in picoplankton." We will now focus on the various mechanisms by which trace and heavy metals are taken up and immobilized within the microbial consortium that are found in the natural aquatic environments. Our approach will be to employ the transmission electron microscope in conjunction with X-ray energy dispersive analysis (EDX), to study bacterial-sized cells and their associated non-cellular particulates. This qualitative and semi-quantitative approach will enable us to analyze cells and cell constituents for their elemental content, and make it possible for us to localize regions in which metal ions become concentrated. Our study over the past year has been fruitful as training ground as we now undertake examination of more complex natural aquatic systems. We will attempt to isolate additional numerically important, metal immobilizing species and study their propensity for metal uptake. We will examine metal polluted aquatic sediments for bacteria and associated particulates, important heavy metal bearing activated sludge and attempt to localize accumulated metals in or on cells making up the biomass. Pure cultures that take up and concentrate a heavy metal have great potential value in the study of mechanisms involved but they also may be developed for use in aspects of water purification, valuable metal recovery or other practical uses. Of greater importance from an environmental standpoint is the fact that a heavy metal can be tracked from a sediment into a bacterial cell mass using the EM-EDX system. Many of the bacteria can also serve as a food supply for grazing protozoa and other invertebrate animals. Our effort in the present proposal will lay a groundwork for these kinds of studies.